JPH08279599A - Preparation of ferroelectricity capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ferroelectric capacitor, by forming a seed layer with perovskite structure by annealing a first ferroelectric film, forming a second ferroeleciric film thereon, and forming a ferroelectric film with perovskite structure by annealing this. SOLUTION: A conductive oxide layer containing RuOx is evaporated on an insulating film 20 of a substrate 10. And a conductive oxide layer (a lower electrode) 30 is completed by thermally processing that in the air. First PZT sol-gel solution is applied on the RuOx lower electrode 30, and a first PZT film is formed. A seed layer 40 is obtained by thermally processing the first PZT film in oxygen atmosphere after baking that. A second ferroelectric film is formed by applying second PZT sol-gel solution on the seed layer 40, and a PZT film 50 is obtained by baking the second ferroelectric film. A PZT film is obtained by annealing that. A RuOx upper electrode 60 is provided by evaporating RuOx on the PZT film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferroelectric capacitor, and more particularly to a FRAM (Ferroelectric Rand).
om Access Memory) and a method of manufacturing a ferroelectric capacitor used as a memory cell.

[0002]

2. Description of the Related Art PZ which is widely used as a ferroelectric substance
T (PbZr1-xTixO3) has a very large polarization value and is excellent in electrical characteristics and material characteristics, but has a disadvantage of poor durability.

Fatigue is a phenomenon in which remanent polarization of a capacitor is reduced by repeated switching and the polarization characteristic of a ferroelectric substance is changed such that the shape of a hysteresis loop is changed.

In order for a capacitor to be used as a memory device, it is required to have durability against recording / reproduction that is repeated in about 10 ¹² cycles. However, a PZT series capacitor that uses Pt (platinum) as an electrode is
After 10 ⁶ cycles, the fatigue phenomenon deepened and 10 ⁹
When it is cycled or longer, the ferroelectric property does not appear and it becomes impossible to function as a capacitor. On the other hand, RuOx
The PZT series ferroelectric capacitor using electrodes has an advantage that it can be used for a long period of time due to its excellent fatigue characteristics. In a capacitor using a RuO _x electrode, a PZT film is formed on the RuO _x electrode by a sol-gel method, but the sol-gel method cannot obtain a PZT film having a uniform thickness and has a pure perovskite phase structure. There was a problem that could not be obtained. After all, according to such a problem, leakage current is small,
That is, it is difficult to manufacture a practical capacitor. However, in the case of a capacitor to which a Pt electrode is applied, a PZT film having a uniform thickness and a pure perovskite phase can be obtained by performing a heat treatment process after forming the PZT film film. On the other hand, in the case of a capacitor using a RuO _x electrode, it is difficult to form a film having a uniform thickness even if a Pt electrode is applied, and it is difficult to form a secondary film called pyrochlore. A lot of phases appear. When the surface of the PZT film is examined in detail with an optical microscope, a rosette structure in which round half points having a radius of about 0.1 to 5 μm are gathered is observed. This rosette structure appears when many perovskite nuclei are not formed. PZ
T is a constituent element of Pb is formed of perovskite nuclei by being lost is diffused into the RuO _x layer becomes difficult of PZT films on RuO _x layer. In order to obtain a PZT film, a PZT film formed by a spin coating method is used in an oxygen atmosphere at 600-7.
Heat in the range of 00 ℃ for about 30 minutes, RTA (rapid
Heating is performed at a temperature of 700 to 850 ° C. by a thermal annealing) process. In such a heat treatment process, Pb is RuO _x
It is believed that the rosette configuration is formed by diffusion inside the layer. As a result of observing the rosette structure, the rosette site is a pure perovskite structure, and the boundary site between these rosettes is pyrochlore (pyrochlor).
It is a mixed structure of e) and perovskite, and the electric current stored in the capacitor leaks through such an interface.
Generally, a capacitor having a RuO _x / PZT / RuO _x laminated structure has a leakage current of 10 ⁻⁵ μA / cm ² or more and Pt /
It is more than 10 times larger than that of a PZT / Pt capacitor, and the surface of the PZT film is not smooth, so it is difficult to perform a process such as etching or forming a multilayer film.

[0005]

It is an object of the present invention to form a ferroelectric film having a pure perovskite structure by suppressing the formation of a rosette structure and making the film thickness uniform. A method of manufacturing a capacitor is provided.

Another object of the present invention is to provide a method of manufacturing a ferroelectric capacitor having excellent fatigue characteristics and a small leakage current.

[0007]

In order to achieve the above object, a method of manufacturing a ferroelectric capacitor according to the present invention comprises (a)
Forming a first ferroelectric film by applying a sol-gel solution including a first ferroelectric substance on the first conductive oxide;
(B) baking the first ferroelectric film,
(C) a step of annealing the first ferroelectric film to form a seed layer having a perovskite structure, and (d) applying a sol-gel solution of a second ferroelectric material to the surface of the seed layer to form a second layer. Forming a ferroelectric film; (e) baking the second ferroelectric film; and (f) annealing the second ferroelectric film to form a ferroelectric film having a perovskite structure. And a step of performing.

In order to achieve the above object, the method of manufacturing a ferroelectric capacitor according to the present invention comprises: (a) applying a first sol-gel solution of a first ferroelectric substance on a RuO _x layer, and Providing a ferroelectric layer, (b) baking the first ferroelectric layer, and (c) annealing the first ferroelectric layer to obtain a perovskite structure seed layer. d) applying a second sol-gel solution of a ferroelectric substance on the seed layer to provide a second ferroelectric layer; and (e) baking the second ferroelectric layer. f) annealing the second ferroelectric layer to obtain a PZT film.

In the manufacturing method of the present invention, the seed layer is preferably as thin as possible.
The range of about 0 to 100 nm is desirable. Then, the application of the PZT sol-gel solution for the ferroelectric film, for example the PZT film, and the baking step of the second ferroelectric layer need to be repeated several times to obtain the desired thickness. In the step of annealing the seed layer and the PZT film, the seed layer and the PZT film having a pure perovskite structure can be formed by instantaneously heating the seed layer and the PZT film at a high temperature in the RTA process.

According to the present invention, the seed layer having the perovskite structure is made of IrO _x , Rh.
O _x, RuO _x, is formed on the surface of the conductive oxide layer made of at least any one of TiO _x, Shidoreya P is in the process of forming, after subsequent PZT film
It assists the growth of the perovskite structure of the ZT film. And,
The surface of the ferroelectric film, that is, the surface of the PZT film becomes very flat.

When a doping agent is added to the PZT sol-gel solution, generation of a desired perovskite structure is promoted, and the doping agent is at least one of Nb, Ta and La.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the accompanying drawings.

As the substrate of the capacitor of the present invention, a Si wafer or a Si wafer having a SiO ₂ film formed to a thickness of 300 nm is used.

Referring first to FIG. 1, the manufacturing method of the present invention comprises the steps of forming a RuO _x bottom electrode, forming a seed layer on the bottom electrode, and forming a ferroelectric film on the seed layer, such as a ferroelectric film. Forming a PZT film, and forming a RuO _x top electrode on the PZT film. The detailed examination of such a stage is as follows.

Referring to FIGS. 2 and 3, Ir is deposited on the insulating film 20 of the substrate 10 by reactive sputtering.
O _x, at least one of RhO _x, RuO _x and TiO _x, preferably depositing a conductive oxide layer containing RuO _x a thickness of 300 nm. Under such conditions for reactive sputtering, the partial pressure ratio of argon and oxygen is 70:30 and the pressure is 200 to 500 mTorr.
, And the power is 200 to 600 W. After the sputtering is completed, the temperature of about 600 ℃ in the atmosphere is about 1
The conductive oxide layer (lower electrode) 30 is completed by heat treatment for a period of time.

In the step of forming a seed layer on the RuO _x film as shown in FIG.
The ZT sol-gel solution is diluted with 1: 1 n-propanol / acetic acid solution to 0.05-0.3M. The prepared first PZT sol-gel solution was applied to the Ru coating using a spin coater.
A first PZT film is formed by applying a predetermined thickness on the O _x lower electrode. At this time, the rotation speed of the spin coater is 2000.
The rotation time is about 40 seconds. The first PZT film thus formed was baked at 250 ° C. for 5 minutes, and then heat-treated in an oxygen atmosphere using a diffusion furnace or an RTA apparatus, and the seed layer 4 was formed as shown in FIG.
Get 0. Seed layer 40 has a thickness of 105 to 70
It is about nm. When the RTA method is applied, the heating rate is 10 to 200 ° C./sec, the heating temperature is 650 to 850 ° C., and the total heat treatment time is preferably 20 to 200 seconds.

After obtaining the seed layer by the above process, PZT prepared as 0.4M on the seed layer and the doped PZT precursor (precur) are prepared.
sor) solution, ie, a second PZT sol-gel solution, is applied on the seed layer to obtain a second ferroelectric film,
The process of baking this is repeated three times, for example, as shown in FIG.
A PZT film 50 having a desired thickness is obtained as shown in FIG. This is annealed in an oxygen atmosphere at 600 to 700 ° C. for 30 minutes, or annealed at 650 to 850 ° C. for 30 seconds by an RTA apparatus, and the temperature rising rate is 10 to 200 ° C./sec. SEM (Scanning Electron Microscopy) and X
As a result of measuring the PZT film obtained by the RD (X-Ray Diffractometer) method, the thickness was about 300 nm, and it was confirmed that a pure perovskite structure was formed. The first and second PZT sol-gel solutions contain a doping agent in a proportion of 0.5 to 7 mol%, and the doping agent promotes the formation of a perovskite structure in the PZT material during annealing. Such doping elements include Nb, Ta, La and the like, and at least one of them can be selected. According to the above doping elements, Pb (NbZr) TiO _x , Pb (TaZ
r) TiO _x or Pb (LaZr) TiO _x is obtained.

Finally, as shown in FIG. 6, the diameter is 75 μm.
R on the PZT film using the shadow mask of
A RuO _x upper electrode 60 is provided by depositing uO _x . As a result of measuring with an optical microscope, the width of the formed electrode is 4.5 ×
The thickness was 10 ⁻⁵ and the thickness was 150 nm.

In the above process, the seed layer is formed of Pb of PZT film of RuO _x Ru component.
PZT, which functions as a diffusion barrier that prevents the components from diffusing into the PZT film and the RuO _x film, respectively.
Serves as a perovskite phase inducer for the film.

In the above process, the present inventor produced three samples, one of which was annealed in the diffusion furnace, the other of which was annealed by the RTA apparatus, and the other of which was annealed. Is manufactured by a conventional method under the same conditions. In measuring the physical properties of two samples according to the invention, the Radient Standard RT66A, R is used for measuring hysteresis loop, durability and leakage current.
The T6000HVS and HP8116A pulse generator manufactured by Hulet Packard were used.

Two manufactured RuO _x / PZT / Ru
As a result of measuring the hysteresis loop of the O _x capacitor,
What was heat-treated by the RTA apparatus showed a better remanent polarization value than that which was heat-treated by the diffusion furnace. Then, in the leakage current, both show similar results, and are 1 / third as compared with the capacitor by the conventional method in which the seed layer is not applied.
A value of 10 ^-6 A / cm ² or less, which is less than 10, was shown. The leakage current value of such a capacitor is almost the same level as that of a Pt / PZT / Pt capacitor using platinum as an electrode material. Then, in measuring the fatigue characteristics, as a result of measuring the fatigue of the capacitor by using a stepped pulse wave of 1 MHz and 5 V, the residual polarization was reduced by about 10% during 10 ¹² switching cycles, and the change in the leakage current value was almost zero. There wasn't. It was also found that the surface of the PZT film has a high smoothness, which is advantageous for etching and formation of a multilayer film generally required for manufacturing a RAM.

[0022]

Example While rotating the spin coater at 4000 RPM, a 0.1 M PZT solution was applied once on the RuO _x film provided on the substrate, and this was baked at 250 ° C. for 5 minutes. Approximately 30 by annealing this with RTA equipment
A seed layer with a thickness of nm was formed. Oxygen is introduced at a rate of 2 liters / min as a heat treatment condition, and the heating rate is 60 ° C.
/ Sec, heat treatment temperature is 750 ° C, heat treatment time is 30
It was seconds.

When the seed layer is completed, spin coater is rotated at 2000 RPM, while the spin coater is rotated to 0.
After applying a 4M PZT solution by spin coating, baking is performed at a temperature of 250 ° C. Such spin coating and baking can be performed with PZ having a desired thickness.
Repeated three times to obtain T film. Then, it heat-processed by RTA apparatus and the PZT film of the perovskite structure which has a thickness of 300 nmnm was obtained. The heat treatment conditions at this time are as follows: oxygen 21 / min, heating rate 60 ° C./se
c, the heat treatment temperature was 750 ° C., and the required time was 30 seconds. The PZT film obtained through such a process has a very smooth surface and no rosette structure is found.
After the heat treatment was completed, a RuO _x upper electrode was formed on the PZT film by a vapor deposition method to measure electrical characteristics. As a result, the remanent polarization value was 20 μC / cm ² , and the remanent polarization value was reduced to less than 10% during 10 ¹² fatigue cycles. The initial leakage current is 5 × 10 ⁻⁷ A / cm.
² and 1.0 × 10 ^-6 A after 10 ¹² fatigue cycles
/ Cm ² was maintained.

[0024]

[Comparative Example] Spin coater 2000R by the conventional method
0.4M PZT on RuO _x film while rotating with PM
The solution is applied and subsequently baked at 250 ° C., but application and baking are repeated three times. Then, heat treatment was performed in a diffusion furnace to obtain a PZT film having a perovskite structure having a thickness of 300 nm. Oxygen is 2 liter / mi as heat treatment condition
The heat treatment temperature is 650 ° C and the time is 30
It was a minute.

The P produced by the conventional method as described above
As a result of measuring the ZT film, the surface of the PZT film was covered with a rosette pattern having a diameter of 0.5 to 1 μm. In addition, to measure the electrical characteristics, PZT
A RuO _x upper electrode was formed on the film. As a result of measuring the electrical characteristics, the residual polarization value was 20 μC / cm ² , and the leakage current level was high. That is, the initial current leakage value is ^{5 × 10 -5 A / cm 2} , the ¹⁰⁹ fatigue cycles since soared to ^{5 × 10 -4 A / cm 2} .

[0026]

As described above, the capacitor according to the present invention having the seed layer not only exhibits lower leakage current than the conventional capacitor without the seed layer, but also has almost the same leakage current as the existing Pt / PZT / Pt capacitor value. They have the same level of leakage current. Also, in terms of fatigue characteristics, the remanent polarization value was P without the seed layer.
It can be seen that the PZT film according to the present invention is larger than the ZT film. Further, since the PZT film according to the present invention does not have a rosette structure, the surface smoothness is higher than that of the conventional PZT film.

[Brief description of drawings]

FIG. 1 is a flowchart of a manufacturing method of the present invention.

FIG. 2 is a process drawing of the manufacturing method of the present invention.

FIG. 3 is a process drawing of the manufacturing method of the present invention.

FIG. 4 is a process drawing of the manufacturing method of the present invention.

FIG. 5 is a process drawing of the manufacturing method of the present invention.

FIG. 6 is a process drawing of the manufacturing method of the present invention.

Claims (26)

[Claims] 1. A step of: (a) applying a sol-gel solution of a first ferroelectric substance on a first conductive oxide to form a first ferroelectric film; and (b) the first ferroelectric film. Baking the conductive film, (c) annealing the first ferroelectric film to form a seed layer having a perovskite structure, and (d) forming a seed ferroelectric layer on the surface of the seed layer. Applying a sol-gel solution to form a second ferroelectric film, (e) baking the second ferroelectric film, and (f) annealing the second ferroelectric film to provide a perovskite structure. And a step of forming a ferroelectric film having: a. 2. The conductive oxide of the first conductive oxide layer is at least one selected from the group consisting of IrO _x , RhO _x , RuO _x, and TiO _x. Item 2. A method for manufacturing a ferroelectric capacitor according to Item 1. 3. The method of manufacturing a ferroelectric capacitor according to claim 1, wherein the oxide layer is provided on a silicon substrate. 4. The method of manufacturing a ferroelectric capacitor according to claim 1, wherein the first oxide layer is provided on a silicon oxide substrate. 5. The method of claim 1, further comprising forming a second conductive oxide layer on the ferroelectric film. 6. The conductive oxide of the second conductive oxide layer is at least one selected from the group consisting of IrO _x , RhO _x , RuO _x, and TiO _x. Item 6. A method for manufacturing a ferroelectric capacitor according to Item 5. 7. The method of manufacturing a ferroelectric capacitor according to claim 1, wherein the seed layer is a PZT layer. 8. The method of manufacturing a ferroelectric capacitor according to claim 1, wherein the ferroelectric film is a PZT film. 9. The seed layer has a thickness of 5 to 7 nm.
The method for manufacturing a ferroelectric capacitor according to claim 1, wherein 10. The method of manufacturing a ferroelectric capacitor according to claim 1, wherein the steps (d) and (e) are repeated many times. 11. The method of manufacturing a ferroelectric capacitor according to claim 1, wherein at least one of the steps (c) and (f) is performed by an RTA apparatus. 12. The heating rate of the RTA apparatus is 10 to 200.
2. Having a range value of ° C / min.
1. A method for manufacturing a ferroelectric capacitor according to 1. 13. The heating temperature of the RTA device is 650-85.
The method for manufacturing a ferroelectric capacitor according to claim 11, having a range value of 0 ° C. 14. The method according to claim 1, wherein at least one of steps (e) and (f) is performed with a heating temperature of 650 to 850 ° C. and a heating time of 20 to 200 seconds. A method of manufacturing the ferroelectric capacitor described. 15. (a) providing a first ferroelectric layer by applying a first sol-gel solution comprising a first ferroelectric substance on the RuO _x layer, and (b) the first ferroelectric layer B), (c) obtaining a seed layer having a perovskite structure by annealing the first ferroelectric layer, and (d) depositing a second sol-gel solution of a ferroelectric substance on the seed layer. Coating to provide a second ferroelectric layer, (e) baking the second ferroelectric layer, and (f) annealing the second ferroelectric layer to obtain a PZT film. A method of manufacturing a ferroelectric capacitor, comprising: 16. (a) A first P on the first conductive oxide layer.
Applying a ZT sol-gel solution to provide a first ferroelectric layer; (b) baking the first ferroelectric layer; and (c) annealing the first ferroelectric layer to form a PZT seed. Obtaining a layer, (d) applying a second PZT sol-gel solution onto the seed layer to provide a second ferroelectric layer, and (e) baking the second ferroelectric layer. (F) Annealing the second ferroelectric layer to obtain a PZT film, the method of manufacturing a ferroelectric capacitor. 17. The first PZT sol-gel solution and a second PZT sol-gel solution
The method of manufacturing a ferroelectric capacitor according to claim 16, wherein any one of the PZT sol-gel solutions contains a doping agent. 18. The method of manufacturing a ferroelectric capacitor according to claim 17, wherein the dopant is one selected from the group consisting of Nb, Ta and La. 19. The method of manufacturing a ferroelectric capacitor according to claim 18, wherein the concentration of the doping agent is in the range of 0.5 to 7 mol%. 20. (a) applying a first PZT sol-gel solution on the RuO _x layer to form a first ferroelectric layer; and (b) baking the first ferroelectric layer. c) annealing the first ferroelectric layer to form a PZT seed layer, and (d) applying a PZT sol-gel solution on the PZT seed layer to form a second ferroelectric layer. And (e) baking the second ferroelectric layer, and (f) annealing the second ferroelectric layer to form a PZT film having a perovskite structure. Manufacturing method of ferroelectric capacitor. 21. The first PZT sol-gel solution and the second PZT sol-gel solution.
21. A doping agent is contained in at least one of the PZT sol-gel solutions.
A method of manufacturing a ferroelectric capacitor as described in 1. 22. The method of manufacturing a ferroelectric capacitor according to claim 21, wherein the dopant is one selected from the group consisting of Nb, Ta and La. 23. The method of manufacturing a ferroelectric capacitor according to claim 22, wherein the concentration of the dopant is in the range of 0.5 to 7 mol%. 24. In the seed layer, the Ru component of RuO _x and the Pb component of a PZT film are the P component, respectively.
3. A diffusion barrier which prevents diffusion into the ZT film and the RuO _x film.
2. The method for manufacturing a ferroelectric capacitor according to 2. 25. The method of claim 22, wherein the seed layer serves as an induction layer that induces a perovskite phase in the PZT film. 26. (a) forming a RuO _x layer on the substrate; and (b) P having a thickness of 5 to 70 nm on the RuO _x layer.
Forming a ZT seed layer, and (c) forming PbZrTiO on the PZT seed layer.
_x , Pb (NbZr) TiO _x , Pb (TaZr) Ti
O _x or Pb (LaZr) strong production method of a dielectric capacitor which comprises a step of forming a ferroelectric layer made of TiO _x.